It would be stupid to claim that environmentalism is never informed by class. Compare, for example, the campaign against patio heaters with the campaign against Agas. Patio heaters are a powerful symbol: heating the atmosphere is not a side-effect, it's their purpose. But to match the fuel consumption of an Aga, a large domestic patio heater would have to run continuously at maximum output for three months a year. Patio heaters burn liquefied petroleum gas, while most Agas use oil, electricity or coal, which produce more CO2. A large Aga running on coal turns out nine tonnes of carbon dioxide per year: 35% more than the total CO2 production of the average UK home. To match that, the patio heater would have to burn for nine months.

So where is the campaign against Agas? There isn't one. I've lost count of the number of aspirational middle-class greens I know who own one of these monsters and believe that they are somehow compatible (perhaps because they look good in a country kitchen) with a green lifestyle. The campaign against Agas - which starts here - will divide rich greens down the middle.

But it is even more stupid to dismiss all environmentalism as a middle-class whim. It's the poor who live beside polluting factories, whose lives are wrecked by opencast mining, who can't afford to move away from motorways or flood zones. They are hit first and worst by climate change. Those who claim that all environmentalists are middle or upper class ignore the tens of millions of peasants and labourers who have mobilised on green issues in south Asia, Africa and Latin America. They indulge a transparent sophistry: some greens are aristocrats; all green issues are therefore the preserve of toffs.

Nowhere is this class-branding more evidently wrong than in the debate over flying. This week the government is expected to announce that a third runway will be built at Heathrow. MPs, airline bosses and rightwing newspapers have been trying to soften us up by insisting that this is happening for the benefit of the poor. Those trying to stop new runways are toffs preventing working-class people from having fun.

The group that has worked hardest to portray the issue this way is the weird cult that arose from the Revolutionary Communist party. This Trotskyist splinter, whose chief theorist is the sociology professor Frank Furedi, has spent the last 30 years moving ever further to the right. The magazine it founded in 1988, Living Marxism (later called LM), celebrated power and demanded total market freedom. It campaigned against bans on tobacco advertising, child pornography and the ownership of handguns. It denied that genocide had taken place in Rwanda, or ethnic cleansing in Bosnia. It provided a platform for writers from the hard-right Institute for Economic Affairs and Centre for the Defence of Free Enterprise. Frank Furedi started writing for the Centre for Policy Studies, which was founded by Keith Joseph and Margaret Thatcher. He and the LM writer Tony Gilland wrote to the supermarket chains, offering - for £7,500 - to educate "consumers about complex scientific issues".

LM closed in 2000, and was replaced by the web magazine Spiked. Edited by Brendan O'Neill, it concentrates on denying the existence of social and environmental problems, and attacking protest movements with a hatred so intense and disproportionate that it must contain an element of self-disgust.

O'Neill, who still describes himself as a Marxist and blogs for the Guardian, calls environmentalism a "death cult" run by "fear-mongering, snobbish, isolationist puritans". The "anti-flying squad" is "illiberal, irrational, parochial, narrow-minded and backward". Plane Stupid's recent protest at Stansted, he says, was motivated by "unabashed, undiluted, unattractive class hatred".

If you understand and accept what climate science is saying, you need no further explanation for protests against airport expansion. But if, like Brendan and his fellow travellers, you refuse to accept that man-made climate change is real, you must show that the campaign to curb it is the result of an irrational impulse. The impulse they choose, because it's an easy stereotype and it suits their prolier-than-thou posturing, is the urge to preserve the wonders of the world for the upper classes. "Cheap flights," O'Neill claims, "has become code for lowlife scum, an issue through which you can attack the 'underclass', the working class and the nouveau riche with impunity."

The connection seems obvious, doesn't it? More cheap flights must be of greatest benefit to the poor. A campaign against airport expansion must therefore be an attack on working-class aspirations. It might be obvious, but it's wrong.

The Sustainable Development Commission collated the figures on passengers using airports in the United Kingdom between 1987 and 2004. During this period, total passenger numbers more than doubled and the price of flights collapsed. The number of people in the lowest two socio-economic categories (D and E) who flew rose, but their proportion fell, from 10% of passengers in 1987 to 8% in 2004. By 2004, there were over five times as many passengers in classes A and B than in classes D and E.

Today, the Civil Aviation Authority's surveys show, the average gross household income of leisure passengers using Heathrow is £59,000 (the national average is £34,660); the average individual income of the airport's business passengers (36% of its traffic) is £83,000. The wealthiest 18% of the population buy 54% of all tickets, the poorest 18% buy 5%.

O'Neill champions Ryanair, Britain's biggest low-cost carrier, as the hero of the working classes. So where would you expect this airline to place most of its advertising? I have the estimated figures for its spending on newspaper ads in 2007. They show that it placed nothing in the Sun, the News of the World, the Mirror, the Star or the Express, but 52% of its press spending went to the Daily Telegraph. Ryanair knows who its main customers are: second-home owners and people who take foreign holidays several times a year.

Who, in the age of the one-penny ticket, is being prevented from flying? It's not because they can't afford the flights that the poor fly less than the rich; it's because they can't afford the second homes in Tuscany, the skiing holidays at Klosters or the scuba diving in the Bahamas. British people already fly twice as much as citizens of the United States, and one fifth of the world's flights use the UK's airports. If people here don't travel, it's not because of a shortage of runways.

At the core of the campaign against a third Heathrow runway are the blue-collar workers and working-class mums of the village of Sipson, whose homes are due to be flattened so that the rich can fly more. If wealthy people don't like living under a flight path, they can move; the poor just have to lump it. Through climate breakdown, the richest people on earth trash the lives of the poorest.

Yes, this is a class war; and Brendan O'Neill and his fellow travellers have sided with the toffs. These Marxist proletarian firebrands are defending the class they profess to hate. Bosses of the world unite, you have nothing to lose but your planes.

• This article was amended on Wednesday 14 January 2009. We said that a large Aga running on coal turns out nine tonnes of carbon dioxide per year: five times the total CO2 production of the average UK home. We meant to say that an Aga produces 35% more than the total CO2 production of the average UK home. This has been corrected.